1. Field of the Invention
The invention relates to a control unit, in particular for use in a motor vehicle. The control unit has a computer, a program memory, a data memory, and timers generating clock signals serving to execute computer programs.
Such control units are used in motor vehicles, for instance, for transmission control, engine control or the like, but can also be used for other purposes. The control units contain a computer, for instance in the form of a microcontroller or microcomputer, that runs application programs specified by the particular intended use.
In the control unit, times must be measured and sequences over time must be controlled. Given the now typical use of operating systems in microcontroller technology, fixed cycle times are often no longer present, or they change frequently. This makes time measurement and chronological sequence control difficult. In conventional control units, either the cycle times are used as a timing pulse, or internal timers in the computer or external timers are used to generate the timing pulse. Timer-counter variables or timer-counter fields are also used, which are supplied with one of the aforementioned timing pulses. Each application in the programs to be executed requires its own timer variable. Time measurement is also dependent on the cycle time or on the resolution of the timer.
U.S. Pat. No. 4,347,570 to Akiyama et al. describes a control unit--embodied as an ignition control system for motor vehicles--wherein the beginning and end of excitation of ignition coils is determined by a microprocessor at fixed time intervals, in dependence on a plurality of engine operating parameters. The main program can be interrupted by three different interrupts, each of different priority.